Preheat oven to 350 degrees Fahrenheit. Grease a 4x8 inch loaf pan. Set aside.
Place butter in a large microwavable dish and place in microwave to melt. Use 30 second increments until butter is fully melted.
Add in ripe bananas and mash with a fork, ensure that butter coats the bananas.
Add baking soda, salt, brown sugar, sour cream, cinnamon, vanilla extract, and large egg to bowl. Stir to combine. Stir in the flour.
Pour batter into greased loaf pan. Bake in preheated oven on center rack for 50 minutes to 1 hour, or until a toothpick entered in the center comes out clean.
Remove from oven and allow bread to cool in pan for about 5 minutes. Then place on cooling rack to allow to cool completely. Enjoy :)